1. Field of the Invention
The present invention relates to an electronic apparatus such as a customized microcontroller and, more particularly, to an electronic apparatus integrating into a single chip such devices as a central processing unit (CPU), a read-only memory (ROM) having programs and data stored fixedly therein and a random access memory (RAM).
2. Description of the Related Art
Heretofore, camera-incorporating video tape recorders (known as camcorders) and like electronic equipment comprise a microcontroller for controlling all or part of their functions, the microcontroller being a one-chip customized LSI electronic device. This type of microcontroller is a customized microcomputer generally composed of a CPU, memories such as ROM and RAM, and peripheral circuits including I/O ports.
The CPU in the microcomputer acts as an address controller for controlling access to the memories or as a processor for executing programs. Stored fixedly in the ROM as firmware is the information by which to control the electronic equipment that incorporates the microcomputer. The RAM offers the CPU a working area and other facilities for program execution. The peripheral circuits deal with communication with the outside. The ROM's, when furnished illustratively as mask ROM's, can significantly reduce the cost of the electronic equipment in which these memories are incorporated.
Over the years, more and more firmware has been stored in the ROM's of electronic devices so as to enhance their performance as well as to make them functionally distinct from their competitors on the market. Utmost care is used to ensure that improved program structures and various checkups keep bugs out of the firmware after its incorporation in mass-produced microcontrollers. Should a bug be detected in mass-produced microcontrollers, the adverse effects thereof need to be corrected by adding an external circuit to the existing devices or by replacing outright the defective devices with bug-free, mass-produced microcontrollers. Such corrections take time, money and human resources. If electronic devices of high packaging density such as camcorders are found to have a bug, it is virtually impossible to correct the bug by adding an external circuit thereto because there is little spare room.